I noticed that the character sheet does not seem to be adding my character's proficiency bonus for the bonus action attack with Spiked Armor for being a 3rd level Battlerager.

 It doesn't say to add your proficiency bonus to that attack.

I don't see anywhere that indicates you should have proficiency in that attack.

It says you can use it as a weapon, but doesn't say it is a simple or martial weapon (of which you are proficient). It says you add STR to that attack and damage (which is already part of the default rules for melee weapon attacks, so this is just reminder), but doesn't say add proficiency.

If it is intended that armor proficiency is supposed to apply to the weapon attack, that is not clear, and since they already included reminder of ability bonus rules, you'd think they would have also added the far less obvious proficiency reminder if that is the case.

The Battlerager is not a particularly impressive barbarian path to begin with. If the spiked armor attack, which is its primary ability, didn't add proficiency to the attack roll it would quickly become useless.

But someone with official capacity has already indicated that the lack of proficiency modifiers in the character builder is a mistake, not on purpose.